1. Technical Field
The present disclosure relates to magnetic media data storage devices. More particularly, the disclosure relates to a system and method for identifying and compensating for non-linear transition shift in magnetic media data storage devices.
2. Related Art
Non-linear transition shift is a phenomenon that affects the timing of the binary transitions of data signals written to the magnetic media in magnetic media data storage devices. When the recording head of a magnetic media data storage device attempts to write a binary transition to the recording medium, the current transition is affected by the magnetic fields of previously written transitions. These magnetic fields can cause the current transition to be shifted in time such that the transition is written either earlier or later than intended. Such time shifts can be a source of noise leading to unacceptable bit error rates when data stored on the magnetic medium are subsequently read back and used by associated data processing equipment.
If the amount of non-linear transition shift affecting a particular binary transition is known in advance, it is possible to compensate for the shift when the transition is written to the magnetic recording medium. For example, if it is known that a particular transition will be delayed by 0.1 nanoseconds, it is possible to write the transition 0.1 nanoseconds earlier. When the timing of a transition is pre-compensated in this manner, the transition will occur precisely where intended when it is subsequently read from the recording medium. A problem, however, is that non-linear transition is inconsistent. The magnetic fields that cause non-linear transition shift depend on the sequence of bits near a particular binary transition. Thus, the amount and direction of non-linear transition shift experienced by a particular binary transition will be dependent on the particular data sequence being written to the magnetic storage medium.
A traditional approach to compensating for non-linear transition shift involves generating a pseudorandom sequence of binary data, writing the pseudorandom sequence to the magnetic recording medium, and reading it back. The recovered sequence is then analyzed to determine the effect that the various bit patterns in the pseudorandom sequence have had on the corresponding binary transitions recorded on the magnetic medium. This traditional approach suffers from a number of drawbacks. The main drawbacks of this approach are that it typically requires over-sampling of the waveforms, it is not very accurate, and only a limited number of data patterns may be specified for defining the associated NLTS values. Furthermore, the compensation values may not be refined over time under actual operating conditions. An improved approach is desirable.